Cooling device

ABSTRACT

A cooling device capable of improving constancy of the ability of a coolant to cool a heat source is provided. A cooling device-cooling an HV device includes a heat exchanger performing heat exchange between the coolant and air-conditioning air; a cooling unit connected in parallel with the heat exchanger and cooling the HV device using the coolant; an expansion valve provided on a downstream side of the heat exchanger and being regulated in opening degree in accordance with a temperature of the coolant between the heat exchanger and the expansion valve and regulating pressure of the coolant flowing through the heat exchanger; and an expansion valve provided on a downstream side of the cooling unit and being regulated in opening degree in accordance with a temperature of the coolant between the cooling unit and the expansion valve and regulating the pressure of the coolant flowing through the cooling unit.

TECHNICAL FIELD

The present invention relates to a cooling device, and particularly to acooling device cooling a heat source utilizing a vapor compressionrefrigeration cycle.

BACKGROUND ART

In recent years, as one of countermeasures against environmentalproblems, attention has been paid to a hybrid vehicle, a fuel cellvehicle, an electric vehicle, and the like running with driving force ofa motor. In such vehicles, electric devices such as a motor, agenerator, an inverter, a converter, and a battery generate heat bytransmission and reception of electric power. Therefore, these electricdevices need to be cooled. Accordingly, there is a proposed techniquefor cooling a heat-generating body utilizing a vapor compressionrefrigeration cycle used as an air-conditioning apparatus for a vehicle.

For example, Japanese Patent Laying-Open No. 2007-69733 (PTD 1)discloses a system for cooling a heat-generating body utilizing acoolant for an air-conditioning apparatus. In the system, a heatexchanger for performing heat exchange with air-conditioning air and aheat exchanger for performing heat exchange with the heat-generatingbody are arranged in parallel on a coolant passage extending from anexpansion valve to a compressor.

Japanese Patent Laying-Open No. 09-290622 (PTD 2) discloses a technique,by which waste heat is recovered from a heat generating portion mountedin a vehicle and causing a coolant for gas injection to absorb heat,thereby effectively improving the heating performance at a relativelylow outside-air temperature while suppressing an increase in powerconsumption. Japanese Patent Laying-Open No. 11-23081 (PTD 3) disclosesa device that is provided with a cooler having a construction in whichintermediate-pressure coolant of a refrigeration cycle cools aheat-generating device, and that is provided with electric expansionvalves that are disposed upstream and downstream of the cooler, suchthat the opening degrees of the valves can be controlled on the basis ofan external signal, wherein a heat-generating device is cooled using theintermediate-pressure coolant.

Japanese Patent Laying-Open No. 2001-309506 (PTD 4) discloses a coolingsystem, in which a coolant of a refrigeration cycle device for vehicleair-conditioning is circulated to a cooling member of an invertercircuit portion for performing a drive control of a vehicle runningmotor, thereby suppressing cooling of air-conditioning air flow by anevaporator of the refrigeration cycle device for vehicleair-conditioning when cooling of the air-conditioning air flow is notrequired. Japanese Patent Laying-Open No. 2005-82066 (PTD 5) discloses acooling system, in which when a coolant is accumulated in an evaporator,a compressor is operated to recover the coolant accumulated in theevaporator, and then, an HV device of the vehicle is started to startthe operation of a pump.

CITATION LIST Patent Document

-   PTD 1: Japanese Patent Laying-Open No. 2007-69733-   PTD 2: Japanese Patent Laying-Open No. 09-290622-   PTD 3: Japanese Patent Laying-Open No. 11-23081-   PTD 4: Japanese Patent Laying-Open No. 2001-309506-   PTD 5: Japanese Patent Laying-Open No. 2005-82066

SUMMARY OF INVENTION Technical Problem

In a vapor compression refrigeration cycle used as an air-conditioningapparatus for a vehicle, a coolant is cooled in a condenser byperforming heat exchange with outside air supplied as wind caused byvehicle running or supplied by draft from a fan. When the amount ofoutside air supplied to the condenser is changed in accordance with therunning state of the vehicle, the temperature of the coolant having beencooled in the condenser is also changed. In addition, the amount ofgenerated heat from a heat source as a target to be cooled is alsogreatly changed in accordance with the running state of the vehicle.Accordingly, it was difficult to keep the constant ability of thecoolant to cool the heat source.

The present invention has been made in light of the above-describedproblems. A main object of the present invention is to provide a coolingdevice capable of improving the constancy of the ability of a coolant tocool a heat source.

Solution to Problem

A cooling device according to the present invention serves to cool aheat source, and includes a compressor compressing a coolant; a firstheat exchanger performing heat exchange between the coolant and outsideair; a decompressor decompressing the coolant; a second heat exchangerperforming heat exchange between the coolant and air-conditioning air; acooling unit connected in parallel with the second heat exchanger andcooling the heat source using the coolant; a first pressure regulatingvalve disposed on a downstream side of the second heat exchanger andregulating pressure of the coolant flowing through the second heatexchanger; and a second pressure regulating valve disposed on adownstream side of the cooling unit and regulating the pressure of thecoolant flowing through the cooling unit. The first pressure regulatingvalve is regulated in opening degree in accordance with a temperature ofthe coolant between the decompressor and the first pressure regulatingvalve. The second pressure regulating valve is regulated in openingdegree in accordance with the temperature of the coolant between thedecompressor and the second pressure regulating valve.

According to the above-described cooling device, preferably, the firstpressure regulating valve is increased in valve opening degree when thetemperature of the coolant between the decompressor and the firstpressure regulating valve is higher than a set value, and decreased invalve opening degree when the temperature of the coolant between thedecompressor and the first pressure regulating valve is lower than theset value. The second pressure regulating valve is increased in valveopening degree when the temperature of the coolant between thedecompressor and the second pressure regulating valve is higher than aset value, and decreased in valve opening degree when the temperature ofthe coolant between the decompressor and the second pressure regulatingvalve is lower than the set value.

The above-described cooling device preferably includes a gas-liquidseparator separating the coolant to be sucked into the compressor intogas and liquid.

According to the above-described cooling device, preferably, thedecompressor includes a first flow rate control valve regulating a flowrate of the coolant flowing into the second heat exchanger, and a secondflow rate control valve regulating the flow rate of the coolant flowinginto the cooling unit.

According to the above-described cooling device, preferably, the firstflow rate control valve is regulated in opening degree in accordancewith a degree of superheat of the coolant on an outlet side of thesecond heat exchanger. The second flow rate control valve is regulatedin opening degree in accordance with the degree of superheat of thecoolant on an outlet side of the cooling unit.

According to the above-described cooling device, preferably, the firstflow rate control valve is increased in valve opening degree when thedegree of superheat of the coolant on the outlet side of the second heatexchanger is higher than a set value, and decreased in valve openingdegree when the degree of superheat of the coolant on the outlet side ofthe second heat exchanger is lower than the set value. The second flowrate control valve is increased in valve opening degree when the degreeof superheat of the coolant on the outlet side of the cooling unit ishigher than a set value, and decreased in valve opening degree when thedegree of superheat of the coolant on the outlet side of the coolingunit is lower than the set value.

Advantageous Effects of Invention

According to the cooling device of the present invention, the constancyof the ability of the coolant to cool the heat source can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing the configuration of a coolingdevice according to the first embodiment.

FIG. 2 is a Mollier chart showing the state of a coolant in a vaporcompression refrigeration cycle.

FIG. 3 is a block diagram showing details of the configuration of acontrol unit.

FIG. 4 is a flowchart illustrating an example of a method of controllingthe cooling device.

FIG. 5 is a Mollier chart illustrating an isothermal line of thecoolant.

FIG. 6 is a schematic diagram showing the configuration of a coolingdevice according to the second embodiment.

FIG. 7 is a Mollier chart showing the state of a coolant in a vaporcompression refrigeration cycle according to the second embodiment.

FIG. 8 is a block diagram showing details of the configuration of acontrol unit according to the second embodiment.

FIG. 9 is a flowchart illustrating an example of a method of controllingthe cooling device according to the second embodiment.

DESCRIPTION OF EMBODIMENTS

The embodiments of the present invention will be hereinafter describedwith reference to the accompanying drawings, in which the same orcorresponding components are designated by the same referencecharacters, and description thereof will not be repeated.

First Embodiment

FIG. 1 is a schematic diagram showing the configuration of a coolingdevice 1 according to the first embodiment. Cooling device 1 accordingto the present embodiment is applied to a hybrid vehicle including, aspower sources, an engine serving as an internal combustion engine and adriving unit serving as an electric motor. This cooling device 1 is usedfor cooling electric devices mounted in the hybrid vehicle. It is to benoted that cooling device 1 of the present invention can be applied notonly to a hybrid vehicle including an engine and an electric motor aspower sources, but also to a vehicle including only an electric motor asa power source (both of which will be collectively referred to as anelectric vehicle).

As shown in FIG. 1, cooling device 1 includes a vapor compressionrefrigeration cycle 10. Vapor compression refrigeration cycle 10 ismounted on a vehicle, for example, to perform cooling in a vehiclecabin. Cooling with use of vapor compression refrigeration cycle 10 isperformed, for example, when a switch for performing cooling is turnedon, or when an automatic control mode for automatically regulating thetemperature in the vehicle cabin at a set temperature is selected andthe temperature in the vehicle cabin is higher than the set temperature.

Vapor compression refrigeration cycle 10 includes a compressor 12, aheat exchanger 14 as the first heat exchanger, an expansion valve 16 asan example of a decompressor, and a heat exchanger 18 as the second heatexchanger.

Compressor 12 is operated by a motor or an engine mounted on a vehicleas a power source and adiabatically compresses the coolant gas to obtainsuperheated coolant gas. Compressor 12 takes in and compresses a coolantflowing from heat exchanger 18 during operation of vapor compressionrefrigeration cycle 10, and then discharges a high-temperature andhigh-pressure gas-phase coolant to coolant passage 21. Compressor 12discharges the coolant to coolant passage 21 to allow circulation of thecoolant through vapor compression refrigeration cycle 10.

Heat exchanger 14 allows superheated coolant gas compressed bycompressor 12 to radiate heat isobarically to an external medium toobtain coolant liquid. The high-pressure gas-phase coolant dischargedfrom compressor 12 is condensed (liquefied) by radiating heat to aperiphery of heat exchanger 14 for cooling. Heat exchanger 14 includes atube through which the coolant flows, and a fin for performing heatexchange between the coolant flowing through the tube and air aroundheat exchanger 14.

Heat exchanger 14 performs heat exchange between cooling air and thecoolant. The cooling air may be supplied to heat exchanger 14 by naturaldraft generated by vehicle running. Alternatively, the cooling air maybe supplied to heat exchanger 14 by forced draft from an outside-airsupplying fan such as a condenser fan 72 or a radiator fan for coolingthe engine. The heat exchange with outside air in heat exchanger 14lowers the temperature of the coolant to liquefy the coolant.

Expansion valve 16 allows the high-pressure liquid-phase coolant flowingthrough coolant passage 25 to be sprayed through a small pore forexpansion to achieve a low-temperature, low-pressure mist-like coolant.Expansion valve 16 decompresses the coolant liquid condensed by heatexchanger 14 to obtain moist vapor in a gas-liquid mixed state. Inaddition, the decompressor for decompressing coolant liquid is notlimited to expansion valve 16 performing throttle expansion, but may bea capillary tube or a control valve whose opening degree can becontrolled.

Heat exchanger 18 performs heat exchange between the coolant andair-conditioning air, to regulate the temperature of theair-conditioning air. By evaporation of the mist-like coolant flowingthrough heat exchanger 18, this heat exchanger 18 absorbs heat ofambient air introduced so as to come in contact with heat exchanger 18.By driving of the air-conditioning fan that is not shown,air-conditioning air is supplied to heat exchanger 18. Theair-conditioning air may be outside air or may be air in the vehiclecabin.

During the cooling operation, heat exchanger 18 uses the coolantdecompressed by expansion valve 16 to absorb heat of evaporation, causedwhen the moist vapor of the coolant is evaporated to become coolant gas,from the air-conditioning air flowing into the vehicle cabin, so thatthe vehicle cabin is cooled. The air-conditioning air with a temperaturelowered due to absorption of heat by heat exchanger 18 is returned againinto the vehicle cabin, so that the vehicle cabin is cooled. Theair-conditioning air is cooled in heat exchanger 18. In heat exchanger18, the coolant absorbs heat from its surroundings by heat transferredfrom the air-conditioning air and is then heated.

Heat exchanger 18 includes a tube through which the coolant flows, and afin for heat exchange between the coolant flowing through the tube andthe ambient air of heat exchanger 18. The coolant in the state of moistvapor flows through the tube. When flowing through the tube, the coolantis evaporated by absorbing heat of the air within the vehicle cabin viathe fin as latent heat of evaporation, and then turned into superheatedvapor by sensible heat. The evaporated coolant is sucked into compressor12. Compressor 12 compresses the coolant in the superheated vapor stateflowing from heat exchanger 18.

Vapor compression refrigeration cycle 10 further includes a coolantpassage 21 allowing communication between compressor 12 and heatexchanger 14, coolant passages 22 and 23 allowing communication betweenheat exchanger 14 and expansion valve 16, a coolant passage 24 allowingcommunication between expansion valve 16 and heat exchanger 18, andcoolant passages 25, 26 and 27 allowing communication between heatexchanger 18 and compressor 12.

Coolant passage 21 is a passage for causing the coolant to flow fromcompressor 12 to heat exchanger 14. The coolant flows between compressor12 and heat exchanger 14 from an outlet of compressor 12 toward an inletof heat exchanger 14 via coolant passage 21. Coolant passages 22 and 23each are a passage for causing the coolant to flow from heat exchanger14 to expansion valve 16. The coolant flows between heat exchanger 14and expansion valve 16 from an outlet of heat exchanger 14 toward aninlet of expansion valve 16 via coolant passages 22 and 23.

Coolant passage 24 is a passage for causing the coolant to flow fromexpansion valve 16 to heat exchanger 18. The coolant flows betweenexpansion valve 16 and heat exchanger 18 from an outlet of expansionvalve 16 toward the inlet of heat exchanger 18 via coolant passage 24.Coolant passages 25 to 27 each are a passage for causing the coolant toflow from heat exchanger 18 to compressor 12. The coolant flows betweenheat exchanger 18 and compressor 12 from the outlet of heat exchanger 18to an inlet of compressor 12 via coolant passages 25 to 27.

Vapor compression refrigeration cycle 10 is configured by compressor 12,heat exchanger 14, expansion valve 16, and heat exchanger 18 coupled viacoolant passages 21 to 27. In addition, the coolant used for vaporcompression refrigeration cycle 10 may be carbon dioxide, hydrocarbonsuch as propane and isobutane, ammonia, fluorocarbons, water or thelike, for example.

An accumulator 60 is disposed on the route of the coolant between heatexchanger 18 and compressor 12. Accumulator 60 separates the coolantflowing out of heat exchanger 18 into a gas-phase coolant and aliquid-phase coolant. Coolant liquid that is a liquid-phase coolant andcoolant vapor that is a gas-phase coolant can be stored withinaccumulator 60. A coolant passage 26 and a coolant passage 27 arecoupled to accumulator 60.

The coolant flowing out of heat exchanger 18 is supplied to accumulator60 through coolant passages 25 and 26. The coolant flowing throughcoolant passage 26 into accumulator 60 is separated into a gas-phasecoolant and a liquid-phase coolant within accumulator 60. When all ofthe coolant does not evaporate in heat exchanger 18 or cooling units 30and 40 described later and the coolant flowing into accumulator 60 is ina gas-liquid two-phase state, accumulator 60 separates the coolant intocoolant liquid in the liquid state and coolant vapor in the gaseousstate, and temporarily stores the separated liquid and vapor therein.The coolant vapor obtained by gas-liquid separation flows out ofaccumulator 60 through coolant passage 27, and is sucked into compressor12.

Coolant passage 27 has an end coupled to the gas-phase side ofaccumulator 60. This end forms an outlet port through which thegas-phase coolant flows out of accumulator 60. Within accumulator 60,the coolant liquid accumulates on the lower side while the coolant vaporaccumulates on the upper side. The end of coolant passage 27 thoughwhich coolant vapor flows out of accumulator 60 is coupled to theceiling portion of accumulator 60. Only the coolant vapor is caused toflow from the ceiling side of accumulator 60 through coolant passage 27to the outside of accumulator 60. Accordingly, accumulator 60 canreliably separate the gas-phase coolant and the liquid-phase coolant.

A pressure regulating valve 19 is provided between heat exchanger 18 andaccumulator 60. Coolant passage 25 forms a route of the coolant betweenheat exchanger 18 and pressure regulating valve 19. Coolant passage 26forms a route of the coolant between pressure regulating valve 19 andaccumulator 60. Pressure regulating valve 19 is a valve provided on thedownstream side of heat exchanger 18 and different from expansion valve16 as a decompressor described above. Pressure regulating valve 19 has afunction as the first pressure regulating valve regulating the pressureof the coolant flowing through heat exchanger 18.

When the opening degree of pressure regulating valve 19 is increased,the pressure loss of the coolant flowing through pressure regulatingvalve 19 becomes relatively small, thereby decreasing the pressuredifference between the coolant flowing through coolant passage 25 andthe coolant flowing through coolant passage 26. Accordingly, thepressure of the coolant flowing through heat exchanger 18 becomes closerto the pressure of the coolant sucked into compressor 12. When theopening degree of pressure regulating valve 19 is relatively large, thepressure of the coolant flowing through heat exchanger 18 becomesrelatively low. By regulating the opening degree of pressure regulatingvalve 19 and controlling pressure regulating valve 19 to be increased inopening degree, the pressure of the coolant flowing through heatexchanger 18 can be lowered.

When the opening degree of pressure regulating valve 19 is decreased,the pressure loss of the coolant flowing through pressure regulatingvalve 19 becomes relatively large, thereby increasing the pressuredifference between the coolant flowing through coolant passage 25 andthe coolant flowing through coolant passage 26. Accordingly, thepressure of the coolant flowing through heat exchanger 18 becomesdifferent from the pressure of the coolant sucked into compressor 12.When the opening degree of pressure regulating valve 19 is relativelysmall, the pressure of the coolant flowing through heat exchanger 18becomes relatively high. By regulating the opening degree of pressureregulating valve 19 and controlling pressure regulating valve 19 to bedecreased in opening degree, the pressure of the coolant flowing throughheat exchanger 18 can be raised.

Coolant passage 25 is provided with a temperature detection unit 52detecting the temperature of the coolant flowing out of heat exchanger18 and into coolant passage 25. Pressure regulating valve 19 iscontrolled in opening degree based on the coolant temperature detectedby temperature detection unit 52. Specifically, when the temperature ofthe coolant flowing through coolant passage 25 is higher than a targetvalue, the opening degree of pressure regulating valve 19 is increased.When the temperature of the coolant flowing through coolant passage 25is lower than the target value, the opening degree of pressureregulating valve 19 is decreased.

Vapor compression refrigeration cycle 10 also includes a receiver 62disposed on the route of the coolant between heat exchanger 14 andexpansion valve 16.

Receiver 62 serves to separate the coolant flowing out of heat exchanger14 into a gas-phase coolant and a liquid-phase coolant. Coolant liquidthat is a liquid-phase coolant and coolant vapor that is a gas-phasecoolant can be stored within receiver 62. Coolant passages 22 and 23 arecoupled to receiver 62.

The coolant flowing out of heat exchanger 14 is supplied to receiver 62through coolant passage 22. The coolant flowing from coolant passage 22into receiver 62 is separated into a gas phase and a liquid phase withinreceiver 62. When all of the coolant does not condense in heat exchanger14 but the coolant flowing into receiver 62 is in a gas-liquid two-phasestate, receiver 62 separates the coolant into coolant liquid in theliquid state and coolant vapor in the gaseous state, and temporarilystores the separated liquid and vapor therein. The coolant liquidobtained by gas-liquid separation flows to the outside of receive 62through coolant passage 23.

Coolant passage 23 has an end coupled to the liquid-phase side ofreceiver 62. This end forms an outlet port through which theliquid-phase coolant flows out of receiver 62. Within receiver 62, thecoolant liquid accumulates on the lower side while the coolant vaporaccumulates on the upper side. Coolant passage 23 has an end throughwhich the coolant liquid is caused to flow out of receiver 62. This endis coupled to the bottom of receiver 62. Only the coolant liquid iscaused to flow from the bottom side of receiver 62 through coolantpassage 23 to the outside of receiver 62. Accordingly, receiver 62 canreliably separate the coolant into a gas-phase coolant and aliquid-phase coolant.

Cooling units 30 and 40 connected in parallel with heat exchanger 18 aredisposed on the route of the coolant flowing from expansion valve 16toward accumulator 60. Cooling device 1 includes a coolant routeconnected in parallel with heat exchanger 18. On this coolant route,cooling units 30 and 40 are provided. Heat exchanger 18 is provided inone of a plurality of passages connected in parallel in the route of thecoolant flowing between expansion valve 16 and accumulator 60. Coolingunit 30 is provided in another passage of the plurality of passages, andcooling unit 40 is provided in still another passage of the plurality ofpassages.

Coolant passages 34 and 44 branch from coolant passage 24 betweenexpansion valve 16 and heat exchanger 18. Coolant passage 34 allowscommunication between coolant passage 24 and cooling unit 30. Thecoolant flows from coolant passage 24 through coolant passage 34 intocooling unit 30. Coolant passage 44 allows communication between coolantpassage 24 and cooling unit 40. The coolant flows from coolant passage24 through coolant passage 44 into cooling unit 40.

Cooling unit 30 includes HV (Hybrid Vehicle) devices 31 and 33 that areelectric devices mounted in an electric vehicle, and a cooling passage32 serving as a pipe line through which a coolant flows. Cooling unit 40includes HV devices 41 and 43 that are electric devices mounted in anelectric vehicle, and a cooling passage 42 serving as a pipe linethrough which a coolant flows. HV devices 31, 33, 41, and 43 each are anexample of a heat source which generates heat by supply and reception ofelectric power.

HV devices 31, 33, 41, and 43 each include, for example, at least anyone of an inverter for converting direct-current (DC) power intoalternate-current (AC) power, a motor generator as a rotating electricmachine, a battery as a power storage device, a boost converter forboosting the voltage of the battery, a DC/DC converter for stepping downthe voltage of the battery, and the like. The battery is a secondarybattery such as a lithium ion battery or a nickel-metal hydride battery.In place of the battery, a capacitor may be employed. For example, HVdevices 31 and 33 each may be an inverter, HV device 41 may be abattery, and HV device 43 may be a capacitor.

The coolant liquid flowing out of receiver 62 flows toward cooling unit30 through coolant passage 34, and flows toward cooling unit 40 throughcoolant passage 44. The coolant reaching cooling units 30 and 40 andflowing through cooling passages 32 and 42 absorbs heat from each of HVdevices 31, 33 and 41, 43, respectively, as heat sources, to cool theseHV devices. Cooling units 30 and 40 cool HV devices 31, 33 and 41, 43,respectively, using the liquid-phase coolant separated in receiver 62.In cooling unit 30, heat is exchanged between the coolant flowingthrough cooling passage 32 and each of HV devices 31 and 33. Also, incooling unit 40, heat is exchanged between the coolant flowing throughcooling passage 42 and each of HV devices 41 and 43. Consequently, HVdevices 31, 33, 41, and 43 are cooled while the coolant is heated.

Cooling units 30 and 40 are provided so as to have structures allowingheat exchange between the coolant and HV devices 31, 33 in coolingpassage 32, and between the coolant and HV devices 41, 43 in coolingpassage 42, respectively. In the present embodiment, cooling units 30and 40 have cooling passages 32 and 42, respectively, formed for examplesuch that the outer peripheral surfaces of cooling passages 32 and 42are brought into direct contact with housings of HV devices 31, 33 and41, 43, respectively. Cooling passages 32 and 42 have portions that areadjacent to the housings of HV devices 31, 33 and 41, 43, respectively.In these portions, heat can be exchanged between the coolant flowingthrough coolant passage 32 and HV devices 31, 33, and also between thecoolant flowing through coolant passage 42 and HV devices 41, 43.

HV devices 31, 33 and 41, 43 are directly connected to the outerperipheral surfaces of cooling passages 32 and 42, respectively, thatform a part of the coolant route extending from expansion valve 16 toaccumulator 60 in vapor compression refrigeration cycle 10. Thus, HVdevices 31, 33 and 41, 43 are cooled. Since HV devices 31, 33 and 41, 43are disposed on the outside of cooling passages 32 and 42, respectively,HV devices 31, 33 and 41, 43 do not interfere with the flow of thecoolant flowing through cooling passages 32 and 42, respectively.Therefore, since the pressure loss of vapor compression refrigerationcycle 10 does not increase, HV devices 31, 33, 41, and 43 can be cooledwithout increasing the motive power of compressor 12.

Alternatively, cooling units 30 and 40 may include optional known heatpipes arranged between HV devices 31, 33 and cooling passage 32, andbetween HV devices 41, 43 and cooling passage 42, respectively. In thiscase, HV devices 31, 33 and 41, 43 are connected to the outer peripheralsurfaces of cooling passages 32 and 42, respectively, via each heatpipe, and cooled by heat transfer from HV devices 31, 33 and 41, 43 tocooling passages 32 and 42, respectively, via each heat pipe. HV devices31, 33, 41, and 43 each are used as a heating unit of the heat pipewhile cooling passages 32 and 42 each are used as a cooling unit of theheat pipe, thereby raising the heat transfer efficiency between coolingpassage 32 and HV devices 31, 33, and between cooling passage 42 and HVdevices 41, 43. Consequently, the cooling efficiency for HV devices 31,33, 41, and 43 can be improved. For example, a wick-type heat pipe canbe used.

Since the heat pipe can reliably transfer heat from HV devices 31, 33and 41, 43 to cooling passages 32 and 42, respectively, HV devices 31,33 and 41, 43 may be spaced apart from cooling passages 32 and 42,respectively. Thus, cooling passages 32 and 42 do not have to bearranged in a complicated manner for bringing cooling passages 32 and 42into contact with HV devices 31, 33 and 41, 43, respectively.Consequently, the degree of freedom in arrangement of HV devices 31, 33,41, and 43 can be improved.

The coolant heated by heat exchange with HV devices 31 and 33 by coolingHV devices 31 and 33 in cooling unit 30 returns to coolant passage 26through coolant passages 35 and 36. The coolant routes connected inparallel with the route of the coolant flowing through heat exchanger 18includes coolant passage 34 on the upstream side of cooling unit 30 (onthe side close to expansion valve 16), cooling passage 32 included incooling unit 30, and coolant passages 35 and 36 on the downstream sideof cooling unit 30 (on the side close to accumulator 60). Coolantpassages 34 and 35 are connected to cooling unit 30. Cooling passage 32has one end connected to coolant passage 34, and the other end connectedto coolant passage 35.

Coolant passage 34 is a passage for allowing communication betweencoolant passage 24 and cooling unit 30, and for causing the coolantcooled at expansion valve 16 to flow into cooling unit 30. The coolantliquid flows from coolant passage 24 through coolant passage 34 intocooling unit 30. Coolant passages 35 and 36 each are a passage forallowing communication between cooling unit 30 and coolant passage 26,and for causing the coolant to flow from cooling unit 30 into coolantpassage 26. The coolant having passed through cooling unit 30 returns tocoolant passage 26 through coolant passages 35 and 36, and reachesaccumulator 60 through coolant passage 26.

A pressure regulating valve 39 is provided between cooling unit 30 andcoolant passage 26. Coolant passage 35 forms a route of the coolantbetween cooling unit 30 and pressure regulating valve 39. Coolantpassage 36 forms a route of the coolant between pressure regulatingvalve 39 and coolant passage 26. Pressure regulating valve 39 is a valveprovided on the downstream side of cooling unit 30 and different fromexpansion valve 16 and pressure regulating valve 19 described above.Pressure regulating valve 39 has a function as the second pressureregulating valve regulating the pressure of the coolant flowing throughcooling unit 30.

When the opening degree of pressure regulating valve 39 is increased,the pressure loss of the coolant flowing through pressure regulatingvalve 39 becomes relatively small, thereby decreasing the pressuredifference between the coolant flowing through coolant passage 35 andthe coolant flowing through coolant passage 36. Accordingly, thepressure of the coolant flowing through cooling unit 30 becomes closerto the pressure of the coolant sucked into compressor 12. When theopening degree of pressure regulating valve 39 is relatively large, thepressure of the coolant flowing through cooling unit 30 becomesrelatively low. By regulating the opening degree of pressure regulatingvalve 39 and controlling pressure regulating valve 39 to be increased inopening degree, the pressure of the coolant flowing through cooling unit30 can be lowered.

When the opening degree of pressure regulating valve 39 is decreased,the pressure loss of the coolant flowing through pressure regulatingvalve 39 becomes relatively large, thereby increasing the pressuredifference between the coolant flowing through coolant passage 35 andthe coolant flowing through coolant passage 36. Accordingly, thepressure of the coolant flowing through cooling unit 30 becomesdifferent from the pressure of the coolant sucked into compressor 12.When the opening degree of pressure regulating valve 39 is relativelysmall, the pressure of the coolant flowing through cooling unit 30becomes relatively high. By regulating the opening degree of pressureregulating valve 39 and controlling pressure regulating valve 39 to bedecreased in opening degree, the pressure of the coolant flowing throughcooling unit 30 can be raised.

Coolant passage 35 is provided with a temperature detection unit 53detecting the temperature of the coolant flowing out of cooling unit 30and into coolant passage 35. Pressure regulating valve 39 is controlledin opening degree based on the temperature of the coolant detected bytemperature detection unit 53. Specifically, the opening degree ofpressure regulating valve 39 is increased when the temperature of thecoolant flowing through coolant passage 35 is higher than a targetvalue; and the opening degree of pressure regulating valve 39 isdecreased when the temperature of the coolant flowing through coolantpassage 35 is lower than the target value.

The coolant heated by heat exchange with HV devices 41 and 43 by coolingHV devices 41 and 43 in cooling unit 40 flows through coolant passages45 and 46 back to coolant passage 26. The coolant routes connected inparallel with the route of the coolant flowing through heat exchanger 18include coolant passage 44 on the upstream side of cooling unit 40 (onthe side close to expansion valve 16), a cooling passage 42 included incooling unit 40, and coolant passages 45 and 46 on the downstream sideof cooling unit 40 (on the side close to accumulator 60). Coolantpassages 44 and 45 are connected to cooling unit 40. Cooling passage 42has one end connected to coolant passage 44, and the other end connectedto coolant passage 45.

Coolant passage 44 is a passage for allowing communication betweencoolant passage 24 and cooling unit 40, and for causing the coolantcooled at expansion valve 16 to flow through cooling unit 40. Thecoolant liquid flows from coolant passage 24 through coolant passage 44into cooling unit 40. Coolant passages 45 and 46 each are a passage forallowing communication between cooling unit 40 and coolant passage 26,and for causing the coolant to flow from cooling unit 40 into coolantpassage 26. The coolant having passed through cooling unit 40 returns tocoolant passage 26 through coolant passages 45 and 46, and reachesaccumulator 60 through coolant passage 26.

A pressure regulating valve 49 is provided between cooling unit 40 andcoolant passage 26. Coolant passage 45 forms a route of the coolantbetween cooling unit 40 and pressure regulating valve 49. Coolantpassage 46 forms a route of the coolant between pressure regulatingvalve 49 and coolant passage 46. Pressure regulating valve 49 is a valveprovided on the downstream side of cooling unit 40 and different fromexpansion valve 16 and pressure regulating valve 19 described above.Pressure regulating valve 49 has a function as the second pressureregulating valve regulating the pressure of the coolant flowing throughcooling unit 40.

When the opening degree of pressure regulating valve 49 is increased,the pressure loss of the coolant flowing through pressure regulatingvalve 49 becomes relatively small, thereby decreasing the pressuredifference between the coolant flowing through coolant passage 45 andthe coolant flowing through coolant passage 46. Accordingly, thepressure of the coolant flowing through cooling unit 40 becomes closerto the pressure of the coolant sucked into compressor 12. When theopening degree of pressure regulating valve 49 is relatively large, thepressure of the coolant flowing through cooling unit 40 becomesrelatively low. By regulating the opening degree of pressure regulatingvalve 49 and controlling pressure regulating valve 49 to be increased inopening degree, the pressure of the coolant flowing through cooling unit40 can be lowered.

When the opening degree of pressure regulating valve 49 is decreased,the pressure loss of the coolant flowing through pressure regulatingvalve 49 becomes relatively large, thereby increasing the pressuredifference between the coolant flowing through coolant passage 45 andthe coolant flowing through coolant passage 46. Accordingly, thepressure of the coolant flowing through cooling unit 40 becomesdifferent from the pressure of the coolant sucked into compressor 12.When the opening degree of pressure regulating valve 49 is relativelysmall, the pressure of the coolant flowing through cooling unit 40becomes relatively high. By regulating the opening degree of pressureregulating valve 49 and controlling pressure regulating valve 49 to bedecreased in opening degree, the pressure of the coolant flowing throughcooling unit 40 can be raised.

Coolant passage 45 is provided with a temperature detection unit 54detecting the temperature of the coolant flowing out of cooling unit 40and into coolant passage 45. Pressure regulating valve 49 is controlledin opening degree based on the coolant temperature detected bytemperature detection unit 54. Specifically, the opening degree ofpressure regulating valve 49 is increased when the temperature of thecoolant flowing through coolant passage 45 is higher than a targetvalue, and the opening degree of pressure regulating valve 49 isdecreased when the temperature of the coolant flowing through coolantpassage 45 is lower than the target value.

FIG. 2 is a Mollier chart showing the state of the coolant in vaporcompression refrigeration cycle 10. In FIG. 2, the horizontal axisdenotes a specific enthalpy of the coolant while the vertical axisdenotes an absolute pressure of the coolant. The unit of the specificenthalpy is kJ/kg and the unit of the absolute pressure is MPa. Thecurve shown in the figure is a saturated vapor line and a saturatedliquid line of the coolant.

FIG. 2 shows a thermal dynamic state of the coolant passing through acoolant circulating flow passage including compressor 12, heat exchanger14, expansion valve 16, and heat exchanger 18 sequentially connected bycoolant passages 21 to 27, and circulating in vapor compressionrefrigeration cycle 10. FIG. 2 also shows a thermal dynamic state of thecoolant flowing through cooling unit 30 connected in parallel with heatexchanger 18 and cooling HV devices 31 and 33 in cooling unit 30. FIG. 2further shows a thermal dynamic state of the coolant flowing throughcooling unit 40 connected in parallel with heat exchanger 18, andcooling HV devices 41 and 43 in cooling unit 40.

As shown in FIG. 2, the coolant in the superheated vapor state takeninto compressor 12 is adiabatically compressed along an isentropic linein compressor 12. As the compression progresses, the coolant rises inpressure and temperature, and turns into high-temperature andhigh-pressure superheated vapor with a high degree of superheat, andthen, flows toward heat exchanger 14. The gas-phase coolant dischargedfrom compressor 12 dissipates heat to the surroundings and is cooled inheat exchanger 14, and thereby condenses (liquefies). Due to heatexchange with outside air in heat exchanger 14, the temperature of thecoolant drops, and the coolant liquefies. The high-pressure coolantvapor flowing into heat exchanger 14 turns from superheated vapor intodry saturated vapor, isobarically, in heat exchanger 14, releases latentheat of condensation, and liquefies gradually to a wet vapor in agas-liquid mixed state. When all the coolant is condensed, it turns intosaturated liquid, and turns into supercooled liquid which has beensupercooled by radiating sensible heat.

Then, the coolant flows into expansion valve 16 through coolant passages22 and 23. At expansion valve 16, the coolant in the supercooled liquidstate undergoes throttle expansion, and the temperature and pressure arelowered without a change in a specific enthalpy, so that low-temperatureand low-pressure moist vapor in the gas-liquid mixed state is obtained.

The coolant in the moist vapor state flowing out of expansion valve 16flows into heat exchanger 18 through coolant passage 24. The coolant inthe moist vapor state flows into the tube of heat exchanger 18. Whenflowing through the tube of heat exchanger 18, the coolant absorbs heatof the air-conditioning air as latent heat of evaporation via the fin,thereby being evaporated while maintaining the equal pressure. When allthe coolant becomes dry saturated vapor, the coolant vapor is furtherincreased in temperature due to the sensible heat, and then, turns intosuperheated vapor.

The coolant in the moist vapor state flowing out of expansion valve 16also flows into cooling passage 32 of cooling unit 30 through coolantpassage 34, and cools HV devices 31 and 33. In cooling unit 30, HVdevices 31 and 33 are cooled by emitting heat to the coolant. By heatexchange with HV devices 31 and 33, the coolant absorbs heat from HVdevices 31 and 33 as latent heat of evaporation, and is thereby heatedand evaporated while maintaining the equal pressure. Thus, the drynessof the coolant is increased. When all the coolant turns into drysaturated vapor, the coolant vapor is further increased in temperatureby sensible heat and turns into superheated vapor.

The coolant in the moist vapor state flowing out of expansion valve 16also flows into cooling passage 42 of cooling unit 40 through coolantpassage 44, and cools HV devices 41 and 43. In cooling unit 40, HVdevices 41 and 43 are cooled by emitting heat to the coolant. By heatexchange with HV devices 41 and 43, the coolant absorbs heat from HVdevices 41 and 43 as latent heat of evaporation, and is thereby heatedand evaporated while maintaining the equal pressure. Thus, the drynessof the coolant is increased. When all the coolant turns into drysaturated vapor, the coolant vapor is further increased in temperatureby sensible heat and turns into superheated vapor.

Then, the coolant is sucked into compressor 12 through accumulator 60.Compressor 12 compresses the gas-phase coolant flowing from accumulator60.

In accordance with such a cycle, the coolant continuously repeats thestate changes of compression, condensation, throttle expansion, andevaporation. In the description of the vapor compression refrigerationcycle set forth above, the theoretical refrigeration cycle is described.However, in actual vapor compression refrigeration cycle 10, loss incompressor 12, and pressure loss and heat loss in the coolant should betaken into consideration.

During the operation of vapor compression refrigeration cycle 10, thecoolant absorbs heat of evaporation from the air-conditioning air forthe vehicle when it evaporates in heat exchanger 18 acting as anevaporator. Thereby, this coolant cools the vehicle cabin. In addition,the low-temperature and low-pressure coolant having undergone throttleexpansion at expansion valve 16 flows into cooling units 30 and 40,exchanges heat with HV devices 31, 33, 41, and 43, thereby cooling HVdevices 31, 33, 41, and 43. Utilizing vapor compression refrigerationcycle 10 for air conditioning in the vehicle cabin, cooling device 1cools HV devices 31, 33, 41, and 43 serving as heat sources mounted inthe vehicle. It is desirable that the temperature required for coolingHV devices 31, 33, 41, and 43 is at least lower than the upper limitvalue of the target temperature range as a temperature range of HVdevices 31, 33, 41, and 43.

Since HV devices 31, 33, 41, and 43 are cooled utilizing vaporcompression refrigeration cycle 10 provided for cooling air-conditioningair in heat exchanger 18, there is no need to provide devices such as adedicated water circulating pump or cooling fan for cooling HV devices31, 33, 41, and 43. Accordingly, since the configuration required forcooling device 1 of HV devices 31, 33, 41, and 43 can be reduced and thedevice configuration can be simplified, the production cost for coolingdevice 1 can be reduced. In addition, since there is no need to operatea power source such as a pump and a cooling fan for cooling HV devices31, 33, 41, and 43, the power consumption for operating the power sourceis not required. Therefore, the power consumption for cooling HV devices31, 33, 41, and 43 can be reduced.

As a route through which the coolant flows from expansion valve 16 toaccumulator 60, a route through which the coolant flows via heatexchanger 18, a route through which the coolant flows via cooling unit30 to cool HV devices 31 and 33, and a route through which the coolantflows via cooling unit 40 to cool HV devices 41 and 43 are arranged inparallel. The low-temperature and low-pressure coolant at the outlet ofexpansion valve 16 is distributed to heat exchanger 18, cooling unit 30and cooling unit 40. The coolant having undergone throttle expansion atexpansion valve 16 is divided into a coolant cooling air-conditioningair in heat exchanger 18, a coolant cooling HV devices 31 and 33 incooling unit 30, and a coolant cooling HV devices 41 and 43 in coolingunit 40.

The pressure of the coolant flowing through heat exchanger 18 iscontrolled by the opening degree of pressure regulating valve 19. Thepressure of the coolant flowing through cooling unit 30 is controlled bythe opening degree of pressure regulating valve 39. The pressure of thecoolant flowing through cooling unit 40 is controlled by the openingdegree of pressure regulating valve 49. By optimally controlling theopening degrees of pressure regulating valves 19, 39 and 49, thepressure of the coolant flowing through each of the coolant routesarranged in parallel can be optimally controlled. FIG. 2 shows the statewhere the coolants flowing through heat exchanger 18 and cooling units30 and 40 are different in pressure, the coolant in the moist vaporstate that has undergone throttle expansion at expansion valve 16 isdivided into three routes arranged in parallel, and the coolants havingpassed through these three routes join again and flow into compressor12.

Receiver 62 is provided on the downstream side of heat exchanger 14. Thecoolant liquid in the supercooled liquid state is stored in thisreceiver 62. Receiver 62 functions as a liquid storage containertemporarily storing coolant liquid that is a liquid-state coolant. Whena prescribed amount of coolant liquid is accumulated in receiver 62having a liquid reservoir function, receiver 62 can serve as a bufferagainst load changes and absorb these load changes. Accordingly, sincethe flow rate of the coolant flowing into cooling units 30 and 40 can bemaintained also while load changes occur, the cooling performance for HVdevices 31, 33, 41, and 43 can be stabilized.

Accumulator 60 is provided on the upstream side of compressor 12. Whenthe coolant flowing into accumulator 60 is not superheated vapor but isin a gas-liquid two-phase state, accumulator 60 functions as agas-liquid separator separating the coolant into a gas phase and aliquid phase. Only the coolant vapor obtained by gas-liquid separationflows out of accumulator 60, so that the coolant sucked into compressor12 is in a gaseous state. Accordingly, it becomes possible to reliablyprevent occurrence of defects such as a failure of compressor 12 causedby a liquid-phase coolant flowing into compressor 12.

Hereinafter described will be details of control of cooling device 1according to the first embodiment. FIG. 3 is a block diagram showingdetails of the configuration of a control unit 80. Control unit 80 shownin FIG. 3 includes an ECU (Electric Control Unit) 81 controlling coolingdevice 1. From temperature input unit 82, ECU 81 receives a signalindicating the temperature of the coolant. Temperature input unit 82receives a signal T1 indicating the temperature of the coolant flowingthrough coolant passage 25 that has been detected by temperaturedetection unit 52, a signal T2 indicating the temperature of the coolantflowing through coolant passage 35 that has been detected by temperaturedetection unit 53, and a signal T3 indicating the temperature of thecoolant flowing through coolant passage 45 that has been detected bytemperature detection unit 54.

Control unit 80 also includes a compressor control unit 85 controllingthe operation of compressor 12 to start and stop, and the rotation speedof this compressor 12; a motor control unit 86 controlling the rotationspeed of motor 74 for rotary drive of condenser fan 72; and an expansionvalve and pressure regulating valve control unit 87 controlling theopening degrees of expansion valve 16 and pressure regulating valves 19,39 and 49. Control unit 80 also includes a memory 84 such as an RAM(Random Access Memory) and an ROM (Read Only Memory). Cooling device 1is controlled by ECU 81 executing various processes in accordance withthe control program stored in memory 84.

Compressor control unit 85 receives a control instruction transmittedfrom ECU 81, and transmits a signal C1 to compressor 12 that instructscompressor 12 to start or stop, or that gives an instruction for therotation speed of compressor 12. Motor control unit 86 receives acontrol instruction transmitted from ECU 81, and transmits a signal M1to motor 74 that gives an instruction for the rotation speed of motor74. Expansion valve and pressure regulating valve control unit 87receives a control instruction transmitted from ECU 81, transmits asignal RV1 to pressure regulating valve 19 that gives an instruction forthe opening degree of pressure regulating valve 19, transmits a signalRV2 to pressure regulating valve 39 that gives an instruction for theopening degree of pressure regulating valve 39, and transmits a signalRV3 to pressure regulating valve 49 that gives an instruction for theopening degree of pressure regulating valve 49. Pressure regulatingvalves 19, 39 and 49 each are an electric expansion valve, and changedin opening degree in accordance with signals RV1, RV2 and RV3,respectively, transmitted from control unit 80. Expansion valve andpressure regulating valve control unit 87 also receives a controlinstruction transmitted from ECU 81 and transmits a signal EV1 to theexpansion valve that gives an instruction for the opening degree ofexpansion valve 16. Expansion valve 16 is changed in opening degree inaccordance with signal EV1 transmitted from control unit 80.

ECU 81 compares each temperature input into temperature input unit 82with the target value of the coolant temperature stored in memory 84. Inaccordance with this comparison result, ECU 81 controls the openingdegrees of pressure regulating valves 19, 39 and 49. ECU 81 has afunction as a valve opening degree regulation unit regulating theopening degrees of pressure regulating valves 19, 39 and 49.

Motor 74 is coupled to condenser fan 72 and drives condenser fan 72 torotate. When the rotation speed of motor 74 is changed, the amount ofheat exchange between the coolant and outside air in heat exchanger 14is controlled. When the rotation speed of motor 74 is increased toincrease the rotation speed of condenser fan 72, the flow rate of theair supplied to heat exchanger 14 is increased, and the amount of heatexchange between the coolant and outside air in heat exchanger 14 isincreased. Consequently, the coolant cooling ability of heat exchanger14 is improved. When the rotation speed of motor 74 is decreased tolower the rotation speed of condenser fan 72, the flow rate of the airsupplied to heat exchanger 14 is decreased, and the amount of heatexchange between the coolant and outside air in heat exchanger 14 isdecreased. Consequently, the coolant cooling ability of heat exchanger14 is deteriorated.

The rotation speed of compressor 12 and the rotation speed of motor 74driving condenser fan 72 for supplying cooling air to heat exchanger 14are controlled appropriately such that coolant liquid may always bestored in receiver 62 and a liquid-state coolant may always be suppliedto cooling units 30 and 40.

FIG. 4 is a flowchart illustrating an example of a method of controllingcooling device 1. FIG. 4 shows an example of the control flow at thetime when the temperature of the coolant flowing through heat exchanger18 and cooling units 30 and 40 are optimally controlled by regulatingthe opening degrees of pressure regulating valves 19, 39 and 49 ofcooling device 1. Although the following description will provide anexplanation of an example in which the opening degree of pressureregulating valve 39 is changed for controlling the temperature of thecoolant flowing through cooling unit 30, other pressure regulatingvalves 19 and 49 are also controlled in the same manner as in theexample described below.

As shown in FIG. 4, the temperature of the coolant flowing throughcooling unit 30 is first read in step (S10). Specifically, temperaturedetection unit 53 is used to detect the temperature of the coolantflowing through coolant passage 35 that has undergone heat exchange withHV devices 31 and 33 in cooling unit 30. Signal T2 indicating thetemperature detected by temperature detection unit 53 is transmittedfrom temperature detection unit 53 to temperature input unit 82, andinput into ECU 81, thereby reading the coolant temperature.

Then, it is determined in step (S20) whether the temperature of thecoolant flowing through cooling unit 30 exceeds a target temperaturevalue or not. When it is determined in step (S20) that the coolanttemperature exceeds the target value, the opening degree of pressureregulating valve 39 is increased in step (S30). In step (S40), thecoolant temperature falls in accordance with this regulation of theopening degree of pressure regulating valve 39. As to the target valueof the coolant temperature, a certain specific temperature may be set asa target value, or a specific temperature range having upper and lowerlimit values may be set as a target value.

FIG. 5 is a Mollier chart illustrating an isothermal line of thecoolant. In FIG. 5, the horizontal axis denotes a specific enthalpy ofthe coolant while the vertical axis denotes an absolute pressure of thecoolant. The unit of the specific enthalpy is kJ/kg and the unit of theabsolute pressure is MPa. The curve shown in the figure is a saturatedvapor line and a saturated liquid line of the coolant. The dotted linein the figure shows an isothermal line of the coolant. The isothermalline on the lower side of the figure shows an isothermal line of thecoolant having a relatively lower temperature while the isothermal lineon the upper side of the figure shows an isothermal line of the coolanthaving a relatively higher temperature.

As has been described with reference to FIG. 2, the coolant cooling HVdevices 31 and 33 in cooling unit 30 flows into cooling unit 30 whilebeing in a gas-liquid two-phase state. This coolant is increased indryness as it is heated by heat exchange with HV devices 31 and 33,thereby turning into dry saturated vapor, and further turning intosuperheated vapor. Most of the coolant flowing through cooling passage32 of cooling unit 30 is in the state of moist vapor in the gas-liquidtwo-phase state. In the gas-liquid two-phase state, as shown in FIG. 5,when the pressure of the coolant is low, the temperature is also low,and when the pressure of the coolant is high, the temperature is alsohigh. In other words, by raising or lowering the pressure of the coolantin the gas-liquid two-phase state, the temperature of the coolant can bearbitrarily raised or lowered.

Thus, when the coolant temperature exceeds a target value, the openingdegree of pressure regulating valve 39 is increased to lower thepressure of the coolant flowing through cooling unit 30, so that thetemperature of the coolant flowing through cooling unit 30 can belowered. The reason why the coolant temperature is high is that thecoolant was excessively heated in cooling unit 30, for example, due to arelatively large amount of generated heat from HV devices 31 and 33, andthe like. In this case, it is considered that HV devices 31 and 33 arenot sufficiently cooled. Therefore, the temperature of the coolantflowing through cooling unit 30 is lowered, to improve the coolingability for HV devices 31 and 33 in cooling unit 30, so that HV devices31 and 33 can be appropriately cooled, and overheating of HV devices 31and 33 can be avoided.

Referring back to FIG. 4, when it is determined in step (S20) that thecoolant temperature is equal to or lower than the target value, it isthen determined in step (S50) whether the temperature of the coolantflowing through cooling unit 30 is lower than the target temperaturevalue or not. When it is determined in step (S50) that the coolanttemperature is lower than the target value, the opening degree ofpressure regulating valve 39 is then decreased in step (S60). In step(S70), the coolant temperature rises in accordance with this regulationof the opening degree of pressure regulating valve 39.

Referring to FIG. 5, when the coolant temperature is lower than thetarget value, the opening degree of pressure regulating valve 39 isdecreased to raise the pressure of the coolant flowing through coolingunit 30, so that the temperature of the coolant flowing through coolingunit 30 can be raised. The reason why the coolant temperature is low isthat the coolant is excessively supplied to cooling unit 30, forexample, due to a relatively small amount of generated heat from I-IVdevices 31 and 33, and the like. In this case, it is considered that HVdevices 31 and 33 are excessively cooled. Therefore, the temperature ofthe coolant flowing through cooling unit 30 is raised to lower thecooling ability for HV devices 31 and 33 in cooling unit 30, so that HVdevices 31 and 33 can be appropriately cooled.

Referring back to FIG. 4, when it is determined in step (S50) that thecoolant temperature is equal to or higher than the target value, thatis, when it is determined that the temperature of the coolant flowingthrough cooling unit 30 is equal to the target temperature, the openingdegree of pressure regulating valve 39 is maintained in step (S80).After steps (S40), (S70) or (S80) shown in FIG. 4, the control flow isreturned to step (S10) in which the coolant temperature is read again.

As described above, in cooling device 1 of the present embodiment,pressure regulating valve 19 is provided on the downstream side of heatexchanger 18, pressure regulating valve 39 is provided on the downstreamside of cooling unit 30, and pressure regulating valve 49 is provided onthe downstream side of cooling unit 40. By regulating the openingdegrees of pressure regulating valves 19, 39 and 49, the temperature ofthe coolant flowing through each of heat exchanger 18 and cooling units30 and 40 can be controlled. By regulating the opening degree ofpressure regulating valve 19, the pressure of the coolant flowingthrough heat exchanger 18 is increased or decreased, and thus, thecoolant temperature is controlled in accordance with the change incoolant pressure. By regulating the opening degree of pressureregulating valve 39, the pressure of the coolant flowing through coolingunit 30 is increased or decreased, and thus, the coolant temperature iscontrolled in accordance with the change in coolant pressure. Byregulating the opening degree of pressure regulating valve 49, thepressure of the coolant flowing through cooling unit 40 is increased ordecreased, and thus, the coolant temperature is controlled in accordancewith the change in coolant pressure.

By optimally controlling the opening degrees of pressure regulatingvalves 19, 39 and 49, the temperature of the coolant flowing througheach of the coolant routes provided in parallel can be optimallycontrolled. Accordingly, it becomes possible to provide a coolant in theoptimal state to each of heat exchanger 18 and cooling units 30 and 40in accordance with the change in the coolant cooling state in heatexchanger 14, the change in the required amount of the cooling operationfor cooling air-conditioning air in heat exchanger 18, the change in theamount of generated heat from HV devices 31, 33, 41, and 43, or thelike. Therefore, the ability to cool HV devices 31, 33, 41, and 43 canbe further equalized, and the constancy of the ability of the coolant tocool the heat source can be improved.

By controlling the state of the coolant such as a temperature of thecoolant flowing through heat exchanger 18 and cooling units 30 and 40,the cooling ability and the cooling efficiency of heat exchanger 18 andcooling units 30 and 40 can be significantly improved. Accordingly,inexpensive cooling device 1 can be provided while easing heatspecifications of HV devices 31, 33, 41, and 43.

Second Embodiment

FIG. 6 is a schematic diagram showing the configuration of a coolingdevice 1 according to the second embodiment. Cooling device 1 of thesecond embodiment is different from cooling device 1 of the firstembodiment shown in FIG. 1 in that expansion valve 16 performingthrottle expansion for the coolant condensed in heat exchanger 14includes three control valves 17, 37 and 47, and accumulator 60 is notprovided. Control valves 17, 37 and 47 are provided on the downstream ofthe branch point at which the route of the liquid coolant flowing out ofreceiver 62 branches into three routes. Control valve 17 is provided incoolant passage 24 on the inlet side of heat exchanger 18. Control valve37 is provided in coolant passage 34 on the inlet side of cooling unit30. Control valve 47 is provided in coolant passage 44 on the inlet sideof cooling unit 40.

Coolant passage 25 is provided with a superheat-degree detection unit 57detecting the degree of superheat of the coolant flowing out of heatexchanger 18 and flowing through coolant passage 25. Control valve 17 iscontrolled in opening degree based on the degree of superheat of thecoolant detected by superheat-degree detection unit 57. Specifically,the opening degree of control valve 17 is increased when the degree ofsuperheat of the coolant flowing through coolant passage 25 is higherthan a target value; and the opening degree of control valve 17 isdecreased when the degree of superheat of the coolant flowing throughcoolant passage 25 is lower than the target value. Control valve 17 hasa function as the first flow rate control valve regulating the flow rateof the coolant flowing into heat exchanger 18.

Coolant passage 35 is provided with a superheat-degree detection unit 58detecting the degree of superheat of the coolant flowing out of coolingunit 30 and flowing through coolant passage 35. Control valve 37 iscontrolled in opening degree based on the degree of superheat of thecoolant detected by superheat-degree detection unit 58. Specifically,the opening degree of control valve 37 is increased when the degree ofsuperheat of the coolant flowing through coolant passage 35 is higherthan a target value; and the opening degree of control valve 37 isdecreased when the degree of superheat of the coolant flowing throughcoolant passage 35 is lower than the target value. Control valve 37 hasa function as the second flow rate control valve regulating the flowrate of the coolant flowing into cooling unit 30.

Coolant passage 45 is provided with a superheat-degree detection unit 59detecting the degree of superheat of the coolant flowing out of coolingunit 40 and flowing through coolant passage 45. Control valve 47 iscontrolled in opening degree based on the degree of superheat of thecoolant detected by superheat-degree detection unit 59. Specifically,the opening degree of control valve 47 is increased when the degree ofsuperheat of the coolant flowing through coolant passage 45 is higherthan a target value; and the opening degree of control valve 47 isdecreased when the degree of superheat of the coolant flowing throughcoolant passage 45 is lower than the target value. Control valve 47 hasa function as the second flow rate control valve regulating the flowrate of the coolant flowing into cooling unit 40.

FIG. 7 is a Mollier chart showing the state of a coolant in a vaporcompression refrigeration cycle 10 according to the second embodiment.In FIG. 7, the horizontal axis denotes a specific enthalpy of thecoolant while the vertical axis denotes an absolute pressure of thecoolant. The unit of the specific enthalpy is kJ/kg and the unit of theabsolute pressure is MPa. The curve shown in the figure is a saturatedvapor line and a saturated liquid line of the coolant.

As shown in FIG. 7, the coolant in a supercooled-liquid state condensedin heat exchanger 14 undergoes throttle expansion so as to reach aprescribed pressure by each of control valves 17, 37 and 47. Thepressure and the temperature of the coolant are regulated by controlvalves 17, 37, and 47 so as to achieve the pressure and the temperaturesuitable to cooling of air-conditioning air in heat exchanger 18,cooling of HV devices 31 and 33 in cooling unit 30, and cooling of HVdevices 41 and 43 in cooling unit 40, respectively.

Control valve 17 serves to decompress the coolant such that the coolanthaving the cooling ability required in heat exchanger 18 can be suppliedto heat exchanger 18. Control valve 37 serves to decompress the coolantsuch that the coolant having the cooling ability required for cooling HVdevices 31 and 33 can be supplied to cooling unit 30. Control valve 47serves to decompress the coolant such that the coolant having thecooling ability required for cooling HV devices 41 and 43 can besupplied to cooling unit 40.

FIG. 8 is a block diagram showing details of the configuration of acontrol unit 80 according to the second embodiment. In addition to theconfiguration of control unit 80 of the first embodiment shown in FIG.3, control unit 80 of the second embodiment includes a superheat-degreeinput unit 83 receiving a signal indicating the degree of superheat ofthe coolant, and a control valve control unit 88 controlling the openingdegrees of control valves 17, 37 and 47. Control unit 80 of the secondembodiment also includes a pressure regulating valve control unit 87controlling pressure regulating valves 19, 39 and 49, in place ofexpansion valve and pressure regulating valve control unit 87 of thefirst embodiment.

Superheat-degree input unit 83 receives a signal SH1 indicating thedegree of superheat of the coolant flowing through coolant passage 25that has been detected by superheat-degree detection unit 57, a signalSH2 indicating the degree of superheat of the coolant flowing throughcoolant passage 35 that has been detected by superheat-degree detectionunit 58, and a signal SH3 indicating the degree of superheat of thecoolant flowing through coolant passage 45 that has been detected bysuperheat-degree detection unit 59.

Control valve control unit 88 receives a control instruction transmittedfrom ECU 81, transmits a signal CV1 to control valve 17 that gives aninstruction for the opening degree of control valve 17, transmits asignal CV2 to control valve 37 that gives an instruction for the openingdegree of control valve 37, and transmits a signal CV3 to control valve47 that gives an instruction for the opening degree of control valve 47.Control valves 17, 37 and 47 are electric valves and changed in openingdegree in accordance with signals CV1, CV2 and CV3, respectively,transmitted from control unit 80.

ECU 81 compares each degree of superheat input into superheat-degreeinput unit 83 with the target value of the degree of superheat of thecoolant stored in memory 84. In accordance with this comparison result,ECU 81 controls the opening degrees of control valves 17, 37 and 47. ECU81 has a function as a control valve opening degree regulation unitregulating the opening degrees of control valves 17, 37 and 47.

FIG. 9 is a flowchart illustrating an example of a method of controllingcooling device 1 according to the second embodiment. FIG. 9 shows anexample of the control flow at the time when the degrees of superheat ofthe coolant flowing out of heat exchanger 18 and cooling units 30 and 40are optimally controlled by regulating the opening degrees of controlvalves 17, 37 and 47, respectively, of cooling device 1. Although thefollowing description will provide an explanation of an example in whichthe opening degree of control valve 37 is changed for controlling thedegree of superheat of the coolant flowing out of cooling unit 30, othercontrol valves 17 and 47 are also controlled in the same manner as inthe example described below.

As shown in FIG. 9, the degree of superheat of the coolant flowingthrough the outlet of cooling unit 30 is first read in step (S110).Specifically, superheat-degree detection unit 58 is used to detect thedegree of superheat of the coolant flowing through coolant passage 35 onthe outlet side of cooling unit 30, which has undergone heat exchangewith HV devices 31 and 33 in cooling unit 30. Signal SH2 indicating thetemperature detected by superheat-degree detection unit 58 istransmitted from superheat-degree detection unit 58 to superheat-degreeinput unit 83, and input into ECU 81, thereby reading the degree ofsuperheat of the coolant.

It is then determined in step (S120) whether the degree of superheat ofthe coolant at the outlet of cooling unit 30 exceeds a target value ofthe degree of superheat or not. When it is determined in step (S120)that the degree of superheat of the coolant exceeds the target value,the opening degree of control valve 37 is then increased in step (S130).In accordance with this regulation of the opening degree of controlvalve 37, the flow rate of the coolant increases in step (S140). Thetarget value of the degree of superheat can be set, for example, suchthat the temperature difference between the superheated vapor and thesaturated vapor under the same pressure falls within a range of 3° C. to5° C. As to the target value of the degree of superheat, a certainspecific degree of superheat may be set as a target value, or a specificrange of the degree of superheat having upper and lower limit values maybe set as a target value.

The reason why the degree of superheat of the coolant is high is thatthe coolant was excessively heated in cooling unit 30, for example, dueto a relatively large amount of generated heat from HV devices 31 and33, and the like. In this case, it is considered that HV devices 31 and33 are not sufficiently cooled. Therefore, the opening degree of controlvalve 37 is increased to increase the flow rate of the coolant flowingthrough cooling unit 30, thereby improving the cooling ability for HVdevices 31 and 33 in cooling unit 30, so that HV devices 31 and 33 canbe appropriately cooled and overheating of HV devices 31 and 33 can beavoided.

When it is determined in step (S120) that the degree of superheat of thecoolant is equal to or lower than the target value, it is thendetermined in step (S150) whether the degree of superheat of the coolantat the outlet of cooling unit 30 is lower than the target value or not.When it is determined in step (S150) that the degree of superheat of thecoolant is lower than the target value, the opening degree of controlvalve 37 is decreased in step (S160). In accordance with this regulationof the opening degree of control valve 37, the flow rate of the coolantdecreases in step (S170).

The reason why the degree of superheat of the coolant is low is that thecoolant is excessively supplied to cooling unit 30, for example, due toa relatively small amount of generated heat from HV devices 31 and 33,and the like. In this case, it is considered that HV devices 31 and 33are excessively cooled. Therefore, the opening degree of control valve37 is decreased to decrease the flow rate of the coolant flowing throughcooling unit 30, thereby lowering the cooling ability for HV devices 31and 33 in cooling unit 30, so that HV devices 31 and 33 can beappropriately cooled.

When it is determined in step (S150) that the degree of superheat of thecoolant is equal to or higher than the target value, that is, when it isdetermined that the degree of superheat of the coolant at the outlet ofcooling unit 30 is equal to the target value, the opening degree ofcontrol valve 37 is maintained in step (S180). After steps (S140),(S170) or (S180) shown in FIG. 9, the control flow is returned to step(S110) in which the degree of superheat is read again.

According to cooling device 1 of the second embodiment described above,control valve 17 is provided on the upstream side of heat exchanger 18,control valve 37 is provided on the upstream side of cooling unit 30,and control valve 47 is provided on the upstream side of cooling unit40. Then, by regulating the opening degrees of control valves 17, 37 and47, the degrees of superheat of the coolant having passed through heatexchanger 18 and cooling units 30 and 40, respectively, can becontrolled. By regulating the opening degree of control valve 17, theflow rate of the coolant flowing through heat exchanger 18 is increasedor decreased, thereby controlling the ability of the coolant to coolair-conditioning air in accordance with the flow rate of the coolant. Byregulating the opening degree of control valve 37, the flow rate of thecoolant flowing through cooling unit 30 is increased or decreased,thereby controlling the ability of the coolant to cool HV devices 31 and33 in accordance with the flow rate of the coolant. By regulating theopening degree of control valve 47, the flow rate of the coolant flowingthrough cooling unit 40 is increased or decreased, thereby controllingthe ability of the coolant to cool HV devices 41 and 43 in accordancewith the flow rate of the coolant.

By optimally controlling the opening degrees of control valves 17, 37and 47, the degree of superheat of the coolant flowing through each ofthe coolant routes provided in parallel can be optimally controlled.Accordingly, it becomes possible to provide an optimum amount of coolantto each of heat exchanger 18 and cooling units 30 and 40 in accordancewith the change in the coolant cooling state in heat exchanger 14, thechange in the required amount of the cooling operation for coolingair-conditioning air in heat exchanger 18, the change in the amount ofgenerated heat from HV devices 31, 33, 41, and 43, or the like. Forexample, when the amount of generated heat from HV devices 41 and 43 isrelatively small while the amount of generated heat from HV devices 31and 33 is relatively large, the opening degrees of control valves 37 and47 only have to be regulated so as to decrease the flow rate of thecoolant supplied to cooling unit 40 and to increase the flow rate of thecoolant supplied to cooling unit 30.

When the minimum necessary coolant is caused to flow into each system,the liquid coolant can be suppressed from accumulating in heat exchanger18 and cooling units 30 and 40, so that distribution of the coolant to aplurality of coolant routes provided in parallel can be optimized. Byregulating the coolant flow rate such that all of the coolant evaporatesin heat exchanger 18 and cooling units 30 and 40, it becomes possible toreliably prevent the coolant in a liquid state from flowing intocompressor 12 to cause a failure in compressor 12. All of the coolantcan be controlled to be in a superheated vapor state while theliquid-phase coolant does not remain at the outlets of heat exchanger 18and cooling units 30 and 40. Accordingly, accumulator 60 for performinggas-liquid separation between the gas-phase coolant and the liquid-phasecoolant can be omitted, so that cooling device 1 can be reduced in cost.

The embodiments set forth above have provided an example in whichtemperature detection units 52, 53 and 54 are provided so as to detectthe temperature of the coolant on the outlet side of each of heatexchanger 18, cooling unit 30 and cooling unit 40, respectively. Thepositions of temperature detection units 52, 53 and 54 are however notlimited to this example, but temperature detection units 52, 53 and 54may be disposed so as to measure the temperature of the coolant at anoptional position as long as the temperature of the coolant betweenexpansion valve 16 and each of pressure regulating valves 19, 39 and 49can be detected. For example, temperature detection unit 52 may detectthe temperature of the coolant flowing through heat exchanger 18,temperature detection unit 53 may detect the temperature of the coolantflowing through cooling passage 32 between HV device 31 and HV device33, and temperature detection unit 54 may detect the temperature of thecoolant flowing through coolant passage 44 on the inlet side of coolingunit 40.

Furthermore, although cooling units 30 and 40 include, as heat sources,two HV devices 31 and 33 and two HV devices 41 and 43, respectively,each cooling unit may include one heat source or any number of heatsources. Furthermore, without being limited to the configuration inwhich two cooling units 30 and 40 are connected in parallel, one coolingunit may be connected in parallel with heat exchanger 18, or three ormore cooling units may be connected in parallel with heat exchanger 18.

In the above-described embodiments, explanations have been given withregard to cooling device 1 cooling electric devices mounted in a vehicleby referring to HV devices 31, 33, 41, and 43 as examples. The electricdevices may be any electric devices as long as they are at leastoperated to generate heat, but are not limited to exemplified electricdevices such as an inverter and a motor generator. In the case where aplurality of electric devices need to be cooled, it is desirable thatthese plurality of electric devices have a common targeted temperaturerange for cooling. The targeted temperature range for cooling is anappropriate temperature range as a temperature environment whereelectric devices are operated.

Furthermore, the heat source cooled by cooling device 1 of the presentinvention is not limited to electric devices mounted in a vehicle, butmay be any device generating heat, or a part of any device generatingheat.

Although the embodiments of the present invention have been described asabove, it should be understood that the embodiments disclosed herein areillustrative and non-restrictive in every respect. The scope of thepresent invention is defined by the terms of the claims, rather than thedescription above, and is intended to include any modifications withinthe meaning and scope equivalent to the terms of the claims.

INDUSTRIAL APPLICABILITY

The cooling device of the present invention may be particularlyadvantageously applied to cooling of an electric device by using a vaporcompression refrigeration cycle for cooling a vehicle cabin in a vehiclesuch as an electric vehicle equipped with electric devices such as amotor generator and an inverter.

REFERENCE SIGNS LIST

1 cooling device, 10 vapor compression refrigeration cycle, 12compressor, 14, 18 heat exchanger, 16 expansion valve, 17, 37, 47control valve, 19, 39, 49 pressure regulating valve, 21, 22, 23, 24, 25,26, 27, 34, 35, 36, 44, 45, 46 coolant passage, 30, 40 cooling unit, 31,33, 41, 43 HV device, 32, 42 cooling passage, 52, 53, 54 temperaturedetection unit, 57, 58, 59 superheat-degree detection unit, 60accumulator, 62 receiver, 80 control unit. 82 temperature input unit, 83superheat-degree input unit, 87 expansion valve and pressure regulatingvalve control unit, 88 control valve control unit.

1. A cooling device cooling a heat source, said cooling devicecomprising: a compressor compressing a coolant; a first heat exchangerperforming heat exchange between said coolant and outside air; adecompressor decompressing said coolant; a second heat exchangerperforming heat exchange between said coolant and air-conditioning air;a cooling unit connected in parallel with said second heat exchanger andcooling said heat source using said coolant; a first pressure regulatingvalve disposed on a downstream side of said second heat exchanger andregulating pressure of said coolant flowing through said second heatexchanger; and a second pressure regulating valve disposed on adownstream side of said cooling unit and regulating the pressure of saidcoolant flowing through said cooling unit, said first pressureregulating valve being regulated in opening degree in accordance with atemperature of said coolant between said decompressor and said firstpressure regulating valve, and said second pressure regulating valvebeing regulated in opening degree in accordance with the temperature ofsaid coolant between said decompressor and said second pressureregulating valve.
 2. The cooling device according to claim 1, whereinsaid first pressure regulating valve is increased in valve openingdegree when the temperature of said coolant between said decompressorand said first pressure regulating valve is higher than a set value, anddecreased in valve opening degree when the temperature of said coolantbetween said decompressor and said first pressure regulating valve islower than the set value, and said second pressure regulating valve isincreased in valve opening degree when the temperature of said coolantbetween said decompressor and said second pressure regulating valve ishigher than a set value, and decreased in valve opening degree when thetemperature of said coolant between said decompressor and said secondpressure regulating valve is lower than the set value.
 3. The coolingdevice according to claim 1, comprising a gas-liquid separatorseparating the coolant to be sucked into said compressor into gas andliquid.
 4. The cooling device according to claim 1, wherein saiddecompressor includes a first flow rate control valve regulating a flowrate of said coolant flowing into said second heat exchanger, and asecond flow rate control valve regulating the flow rate of said coolantflowing into said cooling unit.
 5. The cooling device according to claim4, wherein said first flow rate control valve is regulated in openingdegree in accordance with a degree of superheat of said coolant on anoutlet side of said second heat exchanger, and said second flow ratecontrol valve is regulated in opening degree in accordance with thedegree of superheat of said coolant on an outlet side of said coolingunit.
 6. The cooling device according to claim 5, wherein said firstflow rate control valve is increased in valve opening degree when thedegree of superheat of said coolant on the outlet side of said secondheat exchanger is higher than a set value, and decreased in valveopening degree when the degree of superheat of said coolant on theoutlet side of said second heat exchanger is lower than the set value,and said second flow rate control valve is increased in valve openingdegree when the degree of superheat of said coolant on the outlet sideof said cooling unit is higher than a set value, and decreased in valveopening degree when the degree of superheat of said coolant on theoutlet side of said cooling unit is lower than the set value.